In recent years, an increasing number of users require various electronic equipment especially mobile devices such as cellular phones capable of identifying and operating switches, push-buttons or the like even in dark surroundings by lighting LEDs, EL elements or the like to illuminate the operation panel for a high usability with a cheep price.
The light-guide-sheet and switch using the same for use in such illumination is described with reference to FIGS. 5 and 6. The drawings are shown on an expanded scale in a thickness direction for an easy understanding.
FIG. 5 shows a cross-sectional view of a conventional switch and FIG. 6 shows a perspective view of the light-guide-sheet used in the conventional switch. In the drawing, the conventional switch employs a flexible film-like light-guide-sheet 1 in which the top and bottom surfaces of light-guide-layer 1A are sandwiched between upper protective layer 1B and lower protective layer 1C.
On the top surface of substrate 2 provided with a plurality of wiring patterns (not shown) formed on its top and bottom surfaces, a plurality of stationary contacts 3 are formed that include generally circular central stationary contact 3A and surrounding horseshoe-shaped outside stationary contact 3B.
A plurality of generally dome-shaped movable contacts 4 formed of a thin metal sheet are bonded on stationary contacts 3 by using a sheet (not shown) coated with an adhesive or the like on its bottom surface such that the outside peripheral edges are bonded on outside stationary contacts 3B and the bottom surface center faces central stationary contact 3A with a prescribed clearance.
A plurality of irregularly-shaped light-emitters 1D are formed on light-guide-layer 1A above movable contact 4, and projection 1E is provided on the bottom surface of light-guide-sheet 1 to come into contact with the top surface center of movable contact 4.
Light-emitting-element 5 such as an LED is mounted on substrate 6 on the left side to light-guide-sheet 1, facing its emitting-surface to the left side surface of light-guide-sheet 1, thus forming the conventional switch.
The conventional switch with the above configuration is mounted on an operation panel of electronic equipment, and key-buttons formed from an insulating resin (not shown) is disposed above light-emitters 1D, then central stationary contact 3A and outside stationary contact 3B, light-emitting-elements 5 are connected to electronic circuits (not shown) of the electronic equipment (not shown) via wiring patterns and connectors (not shown) or the like.
In the above configuration, when pressing down a key-button the pressed area of light-guide-sheet 1 bends downward, causing projection 1E to press down the top surface center of generally dome-shaped movable contact 4 to apply a prescribed pressure on the top center of movable contact 4. This reverses movable contact 4 downward elastically with a click feeling, allowing the bottom surface center of movable contact 4 to touch central stationary contact 3A. Therefore, central stationary contact 3A and outside stationary 3B come into the state of electrical connection via movable contact 4.
On the contrary, releasing the downward pressure to the key-button will reverse movable contact 4 upward by an elastic returning force, causing the top surface center of movable contact 4 to depart from central stationary contact 3A and thereby causing central stationary contact 3A and outside stationary 3B to disconnect electrically.
Such electrical connection/disconnection of stationary contacts 3 carries out switching of each function for the equipment accordingly. When a voltage is applied on light-emitting-elements 5 from electronic circuit of the equipment, light-emitting-elements 5 emit light and the light enters into light-guide-layer 1A from the left side surface of light-guide-sheet 1 to illuminate overall light-guide-layer 1A.
Moreover, the light reflected at irregularly-shaped light-emitters 1D in light-guide-layer 1A allows a plurality of light-emitters 1D to illuminate themselves, so that the emitted light illuminates key-buttons (not shown) from below through upper protective layer 1B. Therefore, users can identify and operate key-buttons easily even in dark surroundings.
Japanese Patent Unexamined Publication No. 2006-318905 is known as an example of the Information Disclosure Statement (IDS) relevant to the present invention.
However, in the aforementioned light-guide-sheet and the switch using the same, light-emitting-element 5 is to illuminate the overall light-guide-layer 1A of light-guide-sheet 1, which causes light-emitters 1D located far away from light-emitting-element 5 to become darker due to decrease in light intensity, which tends to cause an uneven illumination.
To reduce the unevenness for a more uniform illumination, many light-emitting-elements are necessary to dispose on the periphery of light-guide-sheet 1 which causes problems of a more complex structure and expensiveness.